Fjellbu was expelled from the Diocese of Nidaros on 1 May 1942, and moved to Hølen before being expelled to Andøya in June 1943. He was coerced from Andøya to Lillehammer in the summer of 1944, but fled to Sweden the same autumn. In December 1944, Fjellbu was appointed Bishop of the liberated parts of Northern Norway by the Norwegian government-in-exile.[1][2] He arrived in Kirkenes on 12 January 1945 and visited the burned-down cities of Vadsø and Vardø as well as other settlements. He stayed in Finnmark until late March, when he was called to London to speak at a memorial sermon in Westminster Abbey on 9 April. He returned from the United Kingdom to Stockholm by plane on 1 May 1945, heading for Finnmark, but due to the events instead travelled to Trondheim by train, arriving on 9 May, and conducting a sermon in a crowded Nidaros Cathedral the following day.[5] A day after Germany's loss in the war, Fjellbu became "Acting Bishop" of Nidaros, and in November 1945 he got the position formally. He was inaugurated on 13 January 1946.[1] During the war years, Fjellbu documented events in a secret diary, parts of which were published as Minner fra krigsårene in 1945.[5]